A typical stent used in clinical practice has an expandable metal wireframe and, accordingly, contains large voids that do not necessarily contribute to either the containment or the compression of plaque. Furthermore, the expansion of the expandable wireframe of the stent may damage the body by morcellating plaque, thereby increasing the risk of plaque causing an embolism in a segment of the body lumen downstream from the stent. For example, even with the development of advanced techniques for removal of plaque at points of stenosis, there may be plaque that remains adherent to the site of stenosis. In these situations, a conventional expandable wireframe stent, due to the force of fluids coursing through the body lumen, may morcellate such residual plaque. Accordingly, there is a need for an improved stent-graft that minimizes the risk of morcellation of plaque from the body lumen.
Stents containing a drug agent have recently been proposed. For example, clinical researchers in the area of coronary artery disease have discovered the benefit of certain drug agents such as paclitaxel and sirolimus. When these drug agents are applied to a typical stent and then placed at previously stenosed regions of a patient's coronary artery, these drugs prevent or slow plaque re-deposition, and/or prevent or slow overly robust neointimal repair, both of which may contribute to restenosis of the artery at the original point of blockage. Currently, the amount of a drug agent that may be applied to a stent is limited and the rate of elution of the drug into the body lumen is rapid. The direction of the elution of the drug is also not controlled, i.e., the drug may elute towards the lumen of the stent as well as towards a body lumen wall. As a result, there is a need for an improved stent-graft that is capable of delivering drug agents towards the blood vessel wall in a controlled manner after the stent-graft is placed in the body lumen.